The extensive use of personal computers and other data processing facilities at home and in the office gave rise to a need for providing voice and data transmission and switching capabilities on a wide spread basis. To satisfy this need, the integrated services digital network (ISDN) was developed for use by telecommunications subscribers. With ISDN service, telecommunication customers have access to two-64 kilobit per second circuit switched B channels and one-16 kilobit per second D channel which is used for packet switching and for the exchange of control information. The B and D channels are multiplexed at customer equipment onto a communication path and are separated at the switching office by a relatively simple demultiplexing stage which applies the B-channels to a circuit switch and the D-channels to a packet switch.
The continuing growth of digital services and capabilities has now created a need for transmission and switching arrangements which have the capacity for larger bandwidths on the order of 150 megabits per second. The high bandwidth can be used for rapidly transmitting large amounts of computer data and for distributing more continuous high bandwidth information such as television signals. In response to the need for higher information bandwidths, a new capability known as broadband ISDN (B-ISDN) is being developed.
B-ISDN standards envision fiber optic connections to both residential and business subscribers which convey packetized information at approximately 150 megabits per second. The high bit rate provides an efficient medium for high bandwidth information while a relatively small packet size, i.e., 53 bytes, provides efficiencies for low bandwidth users such as narrowband voice and ISDN users.
With B-ISDN the header of each packet includes a virtual channel identifier which identifies the communication of which the packet is a part. No separate multiplexed channels of the type used to convey B and D channels in narrowband ISDN (N-ISDN) are used. The mix of packet types on a B-ISDN fiber is not defined and may consist of many nonrelated packets, each conveying narrowband information such as voice or may consist of many related packets all conveying parts of a single high bandwidth information exchange. The design of switching equipment which is capable of switching the diverse traffic mix of B-ISDN is a difficult task.
One possible design for a B-ISDN network would include broadband and narrowband networks and an input stage to separate the different types of traffic onto the different networks. Such a design would be similar to a N-ISDN switching network of the type disclosed in Beckner et al., U.S. Pat. No. 4,592,048. The use of such an input stage to separate traffic is not an efficient design for B-ISDN networks. Traffic separation at the network input requires an additional input switching stage which increases the transfer time of information through the network and adds to the expense of the overall network. The added expense is large in the case of B-ISDN since the input separator stage would not just demultiplex the incoming information stream but would analyze the header of each incoming packet to make separation decisions. Also the separation of information types onto multiple networks, e.g., broadband and narrowband complicates substantially the connection of the information between users of different types.
A need exists in the art for a switching arrangement which can receive a B-ISDN information stream and selectively connect the incoming packetized information to the appropriate broadband and narrowband customers in an efficient and cost effective manner.